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arXiv 2012.11578astro-ph.HE
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LS ~5039中一个假设的冷脉冲星风的性质

Properties of a hypothetical cold pulsar wind in LS~5039

V. Bosch-Ramon

摘要:

LS~5039是一颗强大的伽马射线双星,可能拥有一颗非吸积脉冲星。尽管有丰富的数据,但非热发射器的电源仍然未知。我们使用一个动力辐射的数值模型和多波长的数据来约束的脉冲星风,可能会在LS~5039的非热发射器供电的属性。我们模拟了一种超相对论性(低$B$)冷$e^\pm$风,康普顿散射恒星光子,并与恒星风动态相互作用。能量损失对未受冲击的$e^\pm$ -风动力学的影响,以及两个风接触不连续的几何形状,计算不同的风模型。预测的未冲击$e^\pm$ -风辐射在近星点,预计将是最高的,进行了比较LS~5039数据。来自各向同性冷$e^\pm$风的最小可能辐射以$\sim 3$的因子高估了近星点处的X射线到伽马射线通量。在各向异性风的情况下,如果风轴位于视线的$\lesssim 20-40^\circ$处,则风辐射不会破坏X射线和$\gtrsim 100$ MeV数据($\lesssim 6-24$ \%的概率),取决于各向异性风模型,或者如果风洛伦兹因子$\in 10^2-10^3$,在这种情况下,风力可以更高,但它需要$e^\pm$ -多重数分别为$\sim 10^6$和$10^9$,脉冲星周期为$10^{-2}$ ~s和10~s。所研究的模式预测,低$B$冷脉冲星$e^\pm$ -风LS~5039应该是强各向异性的,要么风洛伦兹因子$\in 10^2-10^3$和非常高的多重数或微调风的方向。低$B$、冷重子主导的风是可能的,但是重子的多重性应该相当低,而重子到$e^\pm$的能量转移在风终止时应该非常有效。强磁化的冷风似乎是最有利的(最不受约束的)选择。

英文摘要:

LS~5039 is a powerful gamma-ray binary that probably hosts a non-accreting pulsar. Despite the wealth of data available, the power source of the non-thermal emitter is still unknown. We use a dynamical-radiative numerical model and multiwavelength data to constrain the properties of a pulsar wind that may power the non-thermal emitter in LS~5039. We ran simulations of an ultrarelativistic (low-$B$) cold $e^\pm$-wind that Compton scatters stellar photons and that dynamically interacts with the stellar wind. The effects of energy losses on the unshocked $e^\pm$-wind dynamics, and the geometry of the two-wind contact discontinuity, are computed for different wind models. The predicted unshocked $e^\pm$-wind radiation at periastron, when expected to be highest, is compared to LS~5039 data. The minimum possible radiation from an isotropic cold $e^\pm$-wind overpredicts the X-ray to gamma-ray fluxes at periastron by a factor of $\sim 3$. In the anisotropic wind case X-ray and $\gtrsim 100$ MeV data are not violated by wind radiation if the wind axis is at $\lesssim 20-40^\circ$ from the line of sight (probability of $\lesssim 6-24$\%), depending on the anisotropic wind model, or if the wind Lorentz factor $\in 10^2-10^3$, in which case the wind power can be higher, but it requires $e^\pm$-multiplicities of $\sim 10^6$ and $10^9$ for a $10^{-2}$~s and 10~s pulsar period, respectively. The studied model predicts that a low-$B$ cold pulsar $e^\pm$-wind in LS~5039 should be strongly anisotropic, with either a wind Lorentz factor $\in 10^2-10^3$ and very high multiplicities or with a fine-tuned wind orientation. A low-$B$, cold baryon-dominated wind would be possible, but then the multiplicities should be rather low, while the baryon-to-$e^\pm$ energy transfer should be very efficient at wind termination. A strongly magnetized cold wind seems to be the most favorable (least constrained) option.

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